JP2012011296A - Method for producing electrode catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a highly-active electrode catalyst which can be obtained by using materials comparatively inexpensive and comparatively large in resource quantities, and can be used even in a high electrical potential in an acidic electrolyte.SOLUTION: The method for producing the electrode catalyst includes a step of firing a precursor of the electrode catalyst, which is obtained by subjecting a mixture containing the following first, second and third materials to a hydrothermal reaction in the presence of water in a supercritical or subcritical state, under such a condition that the following second material is changed into a carbon material. The first material is a metal compound constituted of one or more kinds of metallic elements selected from a group constituted of group 4A elements and group 5A elements, and one or more kinds of non-metallic elements selected from a group constituted of hydrogen, nitrogen, chlorine, carbon, boron, sulfur, and oxygen. The second material is a carbon material precursor, and the third material is a nitrogen-containing compound.

Description

  The present invention relates to a method for producing an electrode catalyst.

  The electrode catalyst is a solid catalyst supported on an electrode (particularly the surface portion of the electrode), and is used in, for example, water electrolysis, organic electrolysis, and fuel cell electrochemical systems. A noble metal is mentioned as an electrode catalyst used in an acidic electrolyte. Among noble metals, platinum is widely used because it is stable even at high potential in an acidic electrolyte.

  However, since platinum is expensive and has a limited amount of resources, there is a need for an electrode catalyst made of a material that is relatively inexpensive and has a relatively large amount of resources.

  Tungsten carbide is known as an electrode catalyst that can be used in an acidic electrolyte at a relatively low cost (see Non-Patent Document 1). Further, as an electrode catalyst that is difficult to dissolve when used at a high potential, an electrode catalyst made of zirconium oxide is known (see Non-Patent Document 2).

Hiroshi Yoneyama et al., “Electrochemistry”, 41, 719 (1973) Yan Liu et al., “Electrochemical and Solid-State Letters” 8 (8), 2005, A400-402.

  The above-mentioned electrode catalyst made of tungsten carbide has a problem that it dissolves at a high potential, and the electrode catalyst made of zirconium oxide has a small current value that can be taken out, and these electrode catalysts are sufficient for use as an electrode catalyst. It can not withstand. An object of the present invention is a method for producing a highly active electrocatalyst that can be obtained using a material that is relatively inexpensive and has a relatively large amount of resources, and that can be used in an acidic electrolyte even at a high potential. Is to provide.

That is, the present invention provides the following means.
<1> Electrocatalyst precursor obtained by hydrothermal reaction of a mixture containing the following first material, the following second material, and the following third material in the presence of supercritical or subcritical water A method for producing an electrocatalyst comprising a step of calcining a body under conditions where the following second material is changed to a carbon material:
The first material is one or more metal elements selected from the group consisting of Group 4A elements and Group 5A elements, and one or more selected from the group consisting of hydrogen, nitrogen, chlorine, carbon, boron, sulfur and oxygen A non-metallic element composed of a metal compound,
The second material is a carbon material precursor,
The third material is a nitrogen-containing compound.
<2> The method according to <1>, wherein the metal element in the first material is Zr or Ti.
<3> The method according to <1> or <2>, wherein the nitrogen-containing compound in the third material is ammonia.
<4> The method according to any one of <1> to <3>, wherein the firing atmosphere is an oxygen-free atmosphere.

  According to the present invention, an electrode catalyst that can be used in an acidic electrolyte even at a high potential and exhibits high activity can be obtained. Moreover, an electrode catalyst can be obtained using a material that is relatively inexpensive and has a relatively large amount of resources, and the present invention is extremely useful industrially.

The schematic diagram which shows the outline | summary of the reaction apparatus (flow-type reaction apparatus) for performing a hydrothermal reaction continuously. The schematic diagram which shows the outline | summary of the reactor in a flow-type reaction apparatus. The powder X-ray diffraction pattern of one Embodiment of the electrode catalyst in this invention is shown. The powder X-ray diffraction pattern of one Embodiment of the electrode catalyst in this invention is shown. The powder X-ray diffraction pattern of one Embodiment of the electrode catalyst in this invention is shown. The powder X-ray diffraction pattern of one Embodiment of the electrode catalyst in this invention is shown. The powder X-ray diffraction pattern of one embodiment of the first material in the present invention is shown. The powder X-ray diffraction pattern of one Embodiment of the electrode catalyst in this invention is shown.

The method for producing an electrocatalyst of the present invention comprises a hydrothermal reaction of a mixture containing the following first material, the following second material, and the following third material in the presence of water in a supercritical state or a subcritical state. A step of calcining the precursor of the electrode catalyst obtained in this manner under the condition that the following second material changes to a carbon material.
The first material is one or more metal elements selected from the group consisting of Group 4A elements and Group 5A elements, and one or more selected from the group consisting of hydrogen, nitrogen, chlorine, carbon, boron, sulfur and oxygen A non-metallic element composed of a metal compound,
The second material is a carbon material precursor,
The third material is a nitrogen-containing compound.

  According to the present invention described above, an electrode catalyst can be obtained using a material that is relatively inexpensive and has a relatively large amount of resources, and in an acidic electrolyte, for example, at a relatively high potential of 0.4 V or more. However, an electrode catalyst having a relatively high activity can be obtained.

  The first material used in the method of the present invention is selected from one or more metal elements selected from the group consisting of Group 4A elements and Group 5A elements, and hydrogen, nitrogen, chlorine, carbon, boron, sulfur and oxygen It is a metal compound comprised with 1 or more types of nonmetallic elements. The metal element in the metal compound of the first material is preferably a metal element of Group 4A element or a metal element of Group 5A element, more preferably Zr, Ti, Ta or Nb, and Zr or Ti. Is preferred. Moreover, the preferable nonmetallic element in the said metal compound is 1 or more types of nonmetallic elements selected from hydrogen, chlorine, and oxygen. Examples of the metal compound when the metal element is Zr include zirconium hydroxide and zirconium oxychloride. Examples of the metal compound when the metal element is Ti include titanium hydroxide, titanium tetrachloride, metatitanic acid, orthotitanic acid, titanium sulfate, and titanium alkoxide.

  The second material used in the method of the present invention is a carbon material precursor. The carbon material precursor can be changed into a carbon material by firing. Examples of the carbon material precursor include sugars such as glucose, fructose, sucrose, cellulose, hydropropylcellulose, glucosamine, chitin, and chitosan, alcohols such as polyvinyl alcohol, glycols such as polyethylene glycol and polypropylene glycol, and polyethylene terephthalate. Nitriles such as polyesters, acrylonitrile, polyacrylonitrile, collagen, keratin, ferritin, various proteins such as hormones, hemoglobin, and albimine, biological materials such as amino acids such as glycine, alanine, methionine, pyrrole, imidazole, pyrazole, isooxazole , Pyridine, pyridazine, pyrimidine, pyrazine, piperidine, piperazine, morpholine and the like Conductor, acetamide, amide compounds such as cyanamide, ascorbic acid, citric acid, stearic acid.

  The third material used in the method of the present invention is a nitrogen-containing compound. The nitrogen-containing compound may be a compound having a nitrogen element excluding the carbonized material precursor. Examples of nitrogen-containing compounds include pyrrole, imidazole, pyrazole, isooxazole, pyridine, pyridazine, pyrimidine, pyrazine, piperidine, piperazine, morpholine and other derivatives, amide compounds such as acetamide and cyanamide, hydroxylamine, sulfuric acid Examples include hydroxylamines such as hydroxylamine, hydrazine anhydride, hydrazine hydrate, hydrazines such as triazane and tetrazane, ammonia, urea, and the like, and ammonia, urea and the like are particularly preferable.

  The third material used in the method of the present invention is preferably contained in an amount of 1000 ppm (ppm represents a part per million by weight, hereinafter the same), preferably 1500 ppm or more, based on the above mixture. More preferably, the content is more preferably 2000 ppm or more.

  In the first invention, the mixture containing the first material, the second material, and the third material is subjected to a hydrothermal reaction in the presence of water in a supercritical state or a subcritical state to produce an electrode catalyst. A precursor is obtained. For the above-described mixing, industrially used apparatuses such as a ball mill, a V-type mixer, and a stirrer can be used. The mixing at this time may be either dry mixing or wet mixing. In addition, after the wet mixing, drying may be performed at a temperature at which the carbon material precursor is not decomposed.

  The supercritical point of water is 374 ° C. and 22 MPa. In the present invention, supercritical water means water under a temperature of 374 ° C. or higher, and preferably has a pressure of 22 MPa or higher. In the present invention, subcritical water means water under a temperature of 250 ° C. or higher, and preferably has a pressure of 20 MPa or higher. In the present invention, as a reaction apparatus for performing the hydrothermal reaction, a batch-type reaction apparatus or a continuous (circulation type) reaction apparatus can be used. In the case of a batch type reaction apparatus, an aqueous solution or slurry is sealed in a reaction vessel, which is kept at a predetermined temperature for a predetermined time, then cooled, and a product produced in the vessel is recovered. As a reaction vessel, it has sufficient heat resistance for a given temperature, has sufficient pressure resistance for the pressure during the reaction, and has a structure with sufficient corrosion resistance for the aqueous solution, slurry, intermediate, or product used Select a material. The material of the reaction vessel may be selected appropriately based on conditions such as the type of aqueous solution or slurry, reaction temperature, pressure, etc. For example, stainless steel such as SUS316, nickel alloy such as Hastelloy and Inconel, or titanium An alloy can be given. Further, the inner surface of the container may be lined with a material having high corrosion resistance such as gold. In order to maintain at a predetermined temperature, for example, an electric furnace can be used. In this case, the electric furnace may be structured such that the reaction container can be inserted into the heating portion of the electric furnace so that operations such as installation and removal of the reaction container can be easily performed. In addition, the reaction vessel may be shaken from the viewpoint of maintaining the uniformity of the contents when raising the temperature and maintaining a predetermined temperature. The pressure in the reaction vessel during the hydrothermal reaction can be adjusted by adjusting the amount of the aqueous solution or slurry put in the reaction vessel according to the predetermined temperature. As a method of cooling the reaction vessel after being held for a predetermined time, there is a method of quenching the reaction vessel by immersing it in water. As a method for recovering the product, the slurry of the contents in the container may be solid-liquid separated, washed and dried, and recovered in a powder state or recovered in a slurry state.

  Below, the reaction apparatus for performing a hydrothermal reaction continuously in this invention is demonstrated, referring drawings. FIG. 1 is a diagram showing an outline of a flow reactor for continuously performing a hydrothermal reaction. The water tanks 11 and 21 are tanks for supplying water. The raw material tank 22 is a tank for supplying the raw material slurry. By opening the valves 110, 210, and 220, liquid is supplied from these tanks. In the case of the first invention, the raw material slurry is a slurry or an aqueous solution of a mixture containing the first material and the second material, and in the case of the second invention, the raw material slurry is a slurry of the first material. Or it is an aqueous solution. The liquid is sent from the water tank 11 to the heater 14 by driving the liquid feed pump 13, and the liquid is sent from the water tank 21 or the raw material tank 22 to the heater 24 by driving the liquid feed pump 23. The sent liquids are mixed in the mixing unit 30 and mainly hydrothermally react in the reactor 40. FIG. 2 is a diagram showing an outline of the reactor. In the reactor 40, there is an internal pipe 41 and a heater 44 for heating the pipe, and the internal pipe 41 is connected to an external pipe. After the hydrothermal reaction, the generated slurry is cooled by the cooler 51, passes through the back pressure valve 53, and is collected in the collection container 60.

  In FIG. 1, the valve 110 and the valve 210 (or valve 220) are opened, the liquid feed pumps 13 and 23 are moved, and the back pressure valve 53 is opened and closed to open the back pressure valve 53 from the liquid feed pumps 13 and 23. The pressure in the pipe can be adjusted. Further, by adjusting the temperatures of the heaters 14 and 24 and the heater 44 in the reactor 40, water in a supercritical state or a subcritical state can be obtained.

  More specifically, the liquid feed pumps 13 and 23 are driven, the pressure in the piping is adjusted as appropriate using the back pressure valve 53, and the temperatures of the heaters 14 and 24 and the heater 44 in the reactor 40 are appropriately adjusted. To adjust the water in the reactor to a supercritical or subcritical state. When the raw material slurry is sent from the raw material tank 22, a hydrothermal reaction is performed in the piping after the mixing unit 30, a hydrothermal reaction product is generated, and the generated slurry can be recovered in the recovery container 60. Further, before and after the raw material slurry is sent from the raw material tank 22, it is possible to send water from the water tank 21 and perform preheating of the piping, cleaning of the piping, and the like. After the hydrothermal reaction, the particle size of the particles in the slurry may be adjusted by removing coarse particles from the produced slurry using the filter 52.

  Further, the reaction time can be adjusted by adjusting the length of the internal piping 41 in the reactor 40. By selecting and using various shapes such as a zigzag shape and a spiral shape as the shape of the internal piping 41, the length of the internal piping 41 can be adjusted.

  The material of the piping and internal piping may be selected appropriately based on the type of raw slurry, the temperature and pressure of the hydrothermal reaction, etc., but as the material, for example, stainless steel such as SUS316 or Hastelloy And nickel alloys such as Inconel, and titanium alloys. Depending on the characteristics of the liquid passing therethrough, part or all of the inner surface of the pipe may be lined with a highly corrosion-resistant material such as gold.

  About the production | generation slurry of the hydrothermal reaction collect | recovered with the collection | recovery container 60, you may use solid-liquid separation, washing | cleaning, and drying, and it may be used in a powder state, and may be used in a slurry state. The hydrothermal reactant is used as a precursor for the electrode catalyst.

  The electrode catalyst in the present invention is obtained by calcining the precursor of the electrode catalyst under conditions where the second material is changed to a carbon material. The firing atmosphere is preferably an oxygen-free atmosphere in order to efficiently synthesize the electrode catalyst, and from the viewpoint of cost, the oxygen-free atmosphere is preferably a nitrogen atmosphere. The furnace used for this firing may be any furnace that can control the atmosphere, such as a tubular electric furnace, tunnel furnace, far-infrared furnace, microwave heating furnace, roller hearth furnace, rotary furnace, etc. It is done. Firing may be performed batchwise or continuously. Alternatively, the electrode catalyst precursor may be fired in a stationary state, or may be fired in a fluid type where the electrode catalyst precursor is fired in a fluid state.

  The firing temperature may be appropriately set in consideration of the type of carbon material precursor and the type of firing atmosphere, but the temperature at which the carbon material precursor changes to a carbon material, that is, the temperature at which the carbon material precursor decomposes and carbonizes. Specifically, the firing temperature is, for example, 400 ° C to 1100 ° C, preferably 500 ° C to 1000 ° C, more preferably 500 ° C to 900 ° C, and still more preferably 700 ° C to 900 ° C. The BET specific surface area of the electrode catalyst can be controlled by controlling the calcination temperature. In the present invention, the condition under which the second material is changed to a carbon material means a condition that can be carbonized to become a carbon material by decomposition of the second material.

  The temperature raising rate during firing is not particularly limited as long as it is in a practical range, and is usually 10 ° C / hour to 600 ° C / hour, preferably 50 ° C / hour to 500 ° C / hour. The temperature may be raised to such a firing temperature at such a heating rate, and the firing may be carried out for 0.1 hours to 24 hours, preferably 1 hour to 12 hours.

The amount of carbon in the electrode catalyst in the present invention is 0.1% by mass or more and 50% by mass or less, more preferably 0.5% by mass or more and 45% by mass or less, and still more preferably 3% by mass or more and 40% by mass or less. Preferably they are 15 to 35 mass%. In the present invention, the Igros value is used as the carbon amount. Specifically, when the electrode catalyst is placed in an alumina crucible and calcined at 1000 ° C. for 3 hours in an air atmosphere, the carbon amount calculated by the following equation: The value of is used.
Carbon amount (mass%) = (W _I −W _A ) / W _I × 100
(Wherein, W _I is an electrode catalyst mass before calcining, the W _A is the weight after baking.)

  The electrode catalyst obtained by the above-described method of the present invention is an electrode catalyst that can be used in an acidic electrolytic solution even at a high potential and can exhibit high activity.

In the present invention, the BET specific surface area of the electrode catalyst is preferably 15 m ² / g or more and 500 m ² / g or less, and more preferably 50 m ² / g or more and 300 m ² / g or less. By setting the BET specific surface area in this way, the activity can be further increased.

In this invention, it is preferable that the carbon coverage calculated | required by the following formula | equation (1) of an electrode catalyst is 0.05 or more and 0.5 or less, More preferably, it is 0.1 or more and 0.3 or less.
Carbon coverage = carbon content (mass%) / BET specific surface area (m ² / g) (1)

  In the present invention, in order to promote the electrode reaction, the work function value of the electrode catalyst is preferably 2 eV or more and 6 eV or less, more preferably 3 eV or more and 5 eV or less. Using a photoelectron spectrometer “AC-2” manufactured by Riken Keiki Co., Ltd. as a work function value, measurement is performed under conditions of light quantity measurement of 500 nW and measurement energy of 4.2 eV to 6.2 eV, and the energy value at the time of current detection is used be able to.

The electrode catalyst obtained by the above-described method of the present invention is composed of a metal compound containing titanium and oxygen and a carbon material covering at least a part of the surface of the compound, and has a BET specific surface area of 15 m ² / g or more and 500 m. ² / g or less is preferable. By using the electrode catalyst as an electrode catalyst for an electrochemical system, a larger oxygen reduction current can be extracted. Titanium is also abundant in resources, which is advantageous for the spread or enlargement of electrochemical systems such as fuel cells. A preferable BET specific surface area of the electrode catalyst is 50 m ² / g or more and 300 m ² / g or less. The metal compound containing titanium and oxygen is preferably titanium oxide, more preferably tetragonal (anatase) titanium oxide. The electrode catalyst can be obtained by using Ti as a metal element in the metal compound in the first invention or the second invention.

The electrode catalyst obtained by the above-described method of the present invention is composed of a metal compound containing zirconium and oxygen and a carbon material covering at least a part of the surface of the compound, and has a BET specific surface area of 15 m ² / g or more and 500 m. ² / g or less is preferable. By using the electrode catalyst as an electrode catalyst for an electrochemical system, a larger oxygen reduction current can be extracted. Zirconium also has abundant resources, which is advantageous for the spread or enlargement of electrochemical systems such as fuel cells. A preferable BET specific surface area of the electrode catalyst is 50 m ² / g or more and 300 m ² / g or less. The metal compound containing zirconium and oxygen is preferably zirconium oxide. The electrode catalyst can be obtained by using Zr as a metal element in the metal compound.

  It can also be set as the electrode catalyst composition which has an electrode catalyst using an electrode catalyst. The electrode catalyst composition usually has a dispersion medium. The electrode catalyst composition can be obtained by dispersing the electrode catalyst in a dispersion medium. Examples of the dispersion medium include alcohols such as methanol, ethanol, isopropanol, and normal propal, and water such as ion exchange water.

  In dispersing, a dispersing agent may be used. Examples of the dispersant include inorganic acids such as nitric acid, hydrochloric acid, and sulfuric acid, organic acids such as oxalic acid, citric acid, acetic acid, malic acid, and lactic acid, water-soluble zirconium salts such as zirconium oxychloride, ammonium polycarboxylate, and polycarboxylic acid. Examples include surfactants such as sodium acid, and catechins such as epicatechin, epigallocatechin, and epigallocatechin galade.

  The electrode catalyst composition may contain an ion exchange resin. In the case of containing an ion exchange resin, the electrode catalyst composition is particularly suitable for a fuel cell. Examples of the ion exchange resin include cation exchange resins such as fluorine ion exchange resins such as Nafion (registered trademark of DuPont) and hydrocarbon ion exchange resins such as sulfonated phenol formaldehyde resins.

  The electrode catalyst composition may contain a conductive material. Examples of the conductive material include carbon black, graphite, graphite, activated carbon, carbon nanotube, carbon nanofiber, carbon nanohorn, fullerene, conductive oxide, conductive oxide fiber, or conductive resin. The electrode catalyst composition of the present invention can also contain a noble metal such as Pt and Ru and a transition metal such as Ni, Fe and Co. When these noble metals and transition metals are contained, the content ratio is preferably a trace amount (for example, about 0.1 to 10 parts by mass with respect to 100 parts by mass of the electrode catalyst).

  In the present invention, the electrode catalyst can be used in an electrochemical system, preferably as an electrode catalyst for a fuel cell, more preferably as an electrode catalyst for a polymer electrolyte fuel cell, and still more preferably as a polymer electrolyte. It can be used as an electrode catalyst for the cathode portion of a fuel cell.

  The electrode catalyst in the present invention can be suitably used at a potential of 0.4 V or more with respect to the reversible hydrogen electrode potential in an acidic electrolyte and is relatively high in activity. And is useful as an oxygen reduction catalyst used to reduce oxygen. A suitable upper limit of the potential when used as an oxygen reduction catalyst can be used up to about 1.6 V, which is a potential for generating oxygen, depending on the stability of the electrode catalyst. When the voltage exceeds 1.6 V, the electrode catalyst is gradually oxidized from the surface simultaneously with the generation of oxygen, and the electrode catalyst may be completely converted into an oxide and deactivated. If the potential is less than 0.4 V, it can be said that it is preferable from the viewpoint of stability of the electrode catalyst, but it may be less useful from the viewpoint of an oxygen reduction catalyst.

  The electrode catalyst composition can be supported on an electrode such as carbon cloth or carbon paper and used for electrolysis of water in an acidic electrolyte, electrolysis of organic matter, or the like. It can also be used by being supported on an electrode constituting a fuel cell such as a polymer electrolyte fuel cell or a phosphoric acid fuel cell.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by these Examples.

In addition, the evaluation method in each Example is as follows.
(1) The BET specific surface area (m ² / g) was determined by a nitrogen adsorption method.
(2) The crystal structure was performed using a powder X-ray diffractometer.
(3) The amount of carbon is obtained by placing the obtained electrode catalyst in an alumina crucible, firing it in a box furnace at 1000 ° C. for 3 hours in the atmosphere, and calculating the carbon amount value (igross value) calculated by the following equation: Using.
Carbon amount (mass%) = (W _I −W _A ) / W _I × 100
(Wherein, W _I is an electrode catalyst mass before calcining, the W _A is the weight after baking.)
(4) The carbon coverage was calculated by the following formula.
Carbon coverage = carbon content (mass%) / BET specific surface area (m ² / g)

Example 1
(Preparation of electrode catalyst)
As a slurry of the first material, metatitanic acid slurry solution (manufactured by Titanium Industry Co., Ltd., AF slurry), as the second material, glucose (manufactured by Kanto Chemical Co., Ltd.), as an aqueous solution containing the third material, NH ₃ water ( Kanto Chemical Co., Ltd., 28.0-30.0 mass%) was used. The solid content concentration of the first material is 0.5% by mass in pure water, the second material glucose is 2.0% by mass, the aqueous NH ₃ water containing the third material is 0.7% by mass, Ketjen Black EC300J (manufactured by Lion Corporation) was added so as to be 0.125% by mass, and dissolved and dispersed to obtain a mixture. After placing 2.5 ml of the mixture in a 5 cc Hastelloy container and sealing the container, the container is placed in an electric furnace heated to 400 ° C. to be in a supercritical state, heated for 10 minutes while shaking, A thermal reaction was performed. After the reaction, cooling was performed, and drying was performed at 60 ° C. for 3 hours to obtain an electrode catalyst precursor. The precursor was placed in an alumina boat and heated while flowing at a flow rate of 1.5 L / min under a nitrogen flow in a tubular electric furnace (manufactured by Motoyama Co., Ltd.) having an internal volume of 13.4 L. The temperature was raised from room temperature (about 25 ° C.) to 800 ° C. at a rate of 300 ° C./hour, and calcined by holding at 800 ° C. for 1 hour to obtain an electrode catalyst 1. The obtained electrode catalyst 1 was titanium oxide coated with carbon. Electrode catalyst 1 had a BET specific surface area of 101 m ² / g, a carbon content of 28% by mass, a carbon coverage of 0.28, and a crystal form of tetragonal system (anatase). FIG. 3 shows a powder X-ray diffraction pattern of this electrode catalyst.

[Evaluation by electrochemical system]
0.02 g of electrode catalyst 1 was weighed, added to a mixed solvent of 5 mL of pure water and 5 mL of isopropyl alcohol, and irradiated with ultrasonic waves to form a suspension. 20 μL of this suspension was applied to a glassy carbon electrode (6 mm diameter, electrode area: 28.3 mm ² ), dried, and then “Nafion (registered trademark)” (manufactured by DuPont, solid content concentration of 5% by mass). After applying 13 μL of the [double diluted sample] and drying, a modified electrode in which the electrode catalyst was supported on the glassy carbon electrode was obtained by treating with a vacuum dryer for 1 hour. This modified electrode is immersed in an aqueous sulfuric acid solution having a concentration of 0.1 mol / L, and is −0.25 to 0.75 V (reversible) with respect to the silver-silver chloride electrode potential at room temperature, atmospheric pressure, oxygen atmosphere and nitrogen atmosphere. The potential was cycled at a scanning speed of 50 mV / s in a scanning range of hydrogen electrode potential conversion 0.025 to 1.025 V). When the current stability at each potential for each cycle was compared and the electrode stability was confirmed, the current value did not fluctuate within the scanning potential range and was stable. Further, when the current values of the oxygen atmosphere and the nitrogen atmosphere at a potential of 0.4 V with respect to the reversible hydrogen electrode potential were compared and the oxygen reduction current was determined, it showed 2345 μA / cm ² per unit area of the electrode. The oxygen reduction current was determined by comparing the current values of the oxygen atmosphere and the nitrogen atmosphere at a potential of .6 V, and it showed 794 μA / cm ² per unit area of the electrode.

Example 2
(Preparation of electrode catalyst)
An electrode catalyst 2 was obtained under the same conditions as in Example 1 except that NH ₃ water was added so as to be 2.0% by mass. Electrode catalyst 1 had a BET specific surface area of 90 m ² / g, a carbon content of 22% by mass, a carbon coverage of 0.24, and a crystal form of tetragonal system (anatase). FIG. 4 shows a powder X-ray diffraction pattern of this electrode catalyst.

[Evaluation by electrochemical system]
0.02 g of electrode catalyst 1 was weighed, added to a mixed solvent of 5 mL of pure water and 5 mL of isopropyl alcohol, and irradiated with ultrasonic waves to form a suspension. 20 μL of this suspension was applied to a glassy carbon electrode (6 mm diameter, electrode area: 28.3 mm ² ), dried, and then “Nafion (registered trademark)” (manufactured by DuPont, solid content concentration of 5% by mass). After applying 13 μL of the [double diluted sample] and drying, a modified electrode in which the electrode catalyst was supported on the glassy carbon electrode was obtained by treating with a vacuum dryer for 1 hour. This modified electrode is immersed in an aqueous sulfuric acid solution having a concentration of 0.1 mol / L, and is −0.25 to 0.75 V (reversible) with respect to the silver-silver chloride electrode potential at room temperature, atmospheric pressure, oxygen atmosphere and nitrogen atmosphere. The potential was cycled at a scanning speed of 50 mV / s in a scanning range of hydrogen electrode potential conversion 0.025 to 1.025 V). When the current stability at each potential for each cycle was compared and the electrode stability was confirmed, the current value did not fluctuate within the scanning potential range and was stable. Further, when the current values of the oxygen atmosphere and the nitrogen atmosphere at a potential of 0.4 V with respect to the reversible hydrogen electrode potential were compared and the oxygen reduction current was determined, it showed 2512 μA / cm ² per unit area of the electrode. The oxygen reduction current was determined by comparing the current values of the oxygen atmosphere and the nitrogen atmosphere at a potential of .6 V, and found to be 1125 μA / cm ² per unit area of the electrode.

Example 3
(Preparation of electrode catalyst)
An electrode catalyst 2 was obtained under the same conditions as in Example 1 except that NH ₃ water was added so as to be 5.5% by mass. Electrode catalyst 1 had a BET specific surface area of 89 m ² / g, a carbon content of 18% by mass, a carbon coverage of 0.20, and a crystal form of tetragonal system (anatase). FIG. 5 shows a powder X-ray diffraction pattern of this electrode catalyst.

[Evaluation by electrochemical system]
0.02 g of electrode catalyst 1 was weighed, added to a mixed solvent of 5 mL of pure water and 5 mL of isopropyl alcohol, and irradiated with ultrasonic waves to form a suspension. 20 μL of this suspension was applied to a glassy carbon electrode (6 mm diameter, electrode area: 28.3 mm ² ), dried, and then “Nafion (registered trademark)” (manufactured by DuPont, solid content concentration of 5% by mass). After applying 13 μL of the [double diluted sample] and drying, a modified electrode in which the electrode catalyst was supported on the glassy carbon electrode was obtained by treating with a vacuum dryer for 1 hour. This modified electrode is immersed in an aqueous sulfuric acid solution having a concentration of 0.1 mol / L, and is −0.25 to 0.75 V (reversible) with respect to the silver-silver chloride electrode potential at room temperature, atmospheric pressure, oxygen atmosphere and nitrogen atmosphere. The potential was cycled at a scanning speed of 50 mV / s in a scanning range of hydrogen electrode potential conversion 0.025 to 1.025 V). When the current stability at each potential for each cycle was compared and the electrode stability was confirmed, the current value did not fluctuate within the scanning potential range and was stable. Further, the current value of the oxygen atmosphere and the nitrogen atmosphere at a potential of 0.4 V with respect to the reversible hydrogen electrode potential was compared, and the oxygen reduction current was obtained. As a result, it showed 2674 μA / cm ² per unit area of the electrode, and 0 The oxygen reduction current was determined by comparing the current values of the oxygen atmosphere and the nitrogen atmosphere at a potential of .6 V. The result showed 1095 μA / cm ² per unit area of the electrode.

Example 4
(Preparation of electrode catalyst)
An electrode catalyst 2 was obtained under the same conditions as in Example 1 except that NH ₃ water was added so as to be 12.3% by mass. Electrode catalyst 1 had a BET specific surface area of 81 m ² / g, a carbon content of 16% by mass, a carbon coverage of 0.20, and a crystal form of tetragonal system (anatase). FIG. 6 shows a powder X-ray diffraction pattern of this electrode catalyst.

[Evaluation by electrochemical system]
0.02 g of electrode catalyst 1 was weighed, added to a mixed solvent of 5 mL of pure water and 5 mL of isopropyl alcohol, and irradiated with ultrasonic waves to form a suspension. 20 μL of this suspension was applied to a glassy carbon electrode (6 mm diameter, electrode area: 28.3 mm ² ), dried, and then “Nafion (registered trademark)” (manufactured by DuPont, solid content concentration of 5% by mass). After applying 13 μL of the [double diluted sample] and drying, a modified electrode in which the electrode catalyst was supported on the glassy carbon electrode was obtained by treating with a vacuum dryer for 1 hour. This modified electrode is immersed in an aqueous sulfuric acid solution having a concentration of 0.1 mol / L, and is −0.25 to 0.75 V (reversible) with respect to the silver-silver chloride electrode potential at room temperature, atmospheric pressure, oxygen atmosphere and nitrogen atmosphere. The potential was cycled at a scanning speed of 50 mV / s in a scanning range of hydrogen electrode potential conversion 0.025 to 1.025 V). When the current stability at each potential for each cycle was compared and the electrode stability was confirmed, the current value did not fluctuate within the scanning potential range and was stable. Further, when the current values of the oxygen atmosphere and the nitrogen atmosphere at a potential of 0.4 V with respect to the reversible hydrogen electrode potential were compared and the oxygen reduction current was determined, it showed 2851 μA / cm ² per unit area of the electrode, and 0 The current values of the oxygen atmosphere and the nitrogen atmosphere at a potential of .6 V were compared, and the oxygen reduction current was determined to be 980 μA / cm ² per unit area of the electrode.

Production Example 1: Slurry preparation of first material (Ti-containing compound) A titanium sulfate (IV) solution (manufactured by Kanto Chemical Co., Ltd., titanium sulfate 24.0% by mass) was adjusted so that the titanium sulfate concentration was 12% by mass. Using an aqueous solution diluted with water and an aqueous solution obtained by diluting NH ₃ water (manufactured by Kanto Chemical Co., Ltd., 28.0 to 30.0% by mass) with water so that the NH ₃ concentration becomes 4% by mass. Neutralization was performed, and the resulting precipitate was filtered and washed to obtain a first material (Ti-containing compound). FIG. 7 shows a powder X-ray diffraction pattern of the first material. This first material was dispersed at a concentration of 1% by mass in an aqueous solution prepared with water so that NH ₃ was 0.7% by mass to obtain a Ti-containing compound slurry.

Example 5
(Preparation of electrode catalyst)
The Ti-containing compound slurry obtained in Production Example 1 was used as the first material slurry. Glucose (manufactured by Kanto Chemical Co., Inc.) is used as the second material, NH ₃ water (manufactured by Kanto Chemical Co., Ltd., 28.0 to 30.0% by mass) is used as the aqueous solution containing the third material, and others. As the material, Ketjen Black EC300J (manufactured by Lion Corporation) was used. In an aqueous solution adjusted with water so that NH ₃ water, which is an aqueous solution containing the third material, is 0.7% by mass, glucose is dissolved at a concentration of 4% by mass and Ketjen Black EC300J is 0.025% by mass. Dispersion was performed to obtain second material, third material and other material-containing solutions. 1.25 ml each of the Ti-containing compound slurry, the second material, the third material, and the other material-containing solution were placed in a Hastelloy container having an internal volume of 5 cc to obtain a mixture. After sealing the vessel, it was placed in an electric furnace heated to 400 ° C. to be in a supercritical state, heated for 10 minutes with shaking, and subjected to a hydrothermal reaction. After the reaction, cooling was performed, and drying was performed at 60 ° C. for 3 hours to obtain an electrode catalyst precursor. The precursor was placed in an alumina boat and heated while flowing at a flow rate of 1.5 L / min under a nitrogen flow in a tubular electric furnace (manufactured by Motoyama Co., Ltd.) having an internal volume of 13.4 L. The temperature was raised from room temperature (about 25 ° C.) to 800 ° C. at a rate of 300 ° C./hour, and calcined by holding at 800 ° C. for 1 hour to obtain an electrode catalyst 1. The obtained electrode catalyst 1 was titanium oxide coated with carbon. Electrode catalyst 1 had a BET specific surface area of 100 m ² / g, a carbon content of 22% by mass, a carbon coverage of 0.22, and a crystal form of tetragonal system (anatase). FIG. 8 shows a powder X-ray diffraction pattern of this electrode catalyst.

[Evaluation by electrochemical system]
0.02 g of electrode catalyst 1 was weighed, added to a mixed solvent of 5 mL of pure water and 5 mL of isopropyl alcohol, and irradiated with ultrasonic waves to form a suspension. 20 μL of this suspension was applied to a glassy carbon electrode (6 mm diameter, electrode area: 28.3 mm ² ), dried, and then “Nafion (registered trademark)” (manufactured by DuPont, solid content concentration of 5% by mass). After applying 13 μL of the [double diluted sample] and drying, a modified electrode in which the electrode catalyst was supported on the glassy carbon electrode was obtained by treating with a vacuum dryer for 1 hour. This modified electrode is immersed in an aqueous sulfuric acid solution having a concentration of 0.1 mol / L, and is −0.25 to 0.75 V (reversible) with respect to the silver-silver chloride electrode potential at room temperature, atmospheric pressure, oxygen atmosphere and nitrogen atmosphere. The potential was cycled at a scanning speed of 50 mV / s in a scanning range of hydrogen electrode potential conversion 0.025 to 1.025 V). When the current stability at each potential for each cycle was compared and the electrode stability was confirmed, the current value did not fluctuate within the scanning potential range and was stable. Further, when the current values of the oxygen atmosphere and the nitrogen atmosphere at a potential of 0.4 V with respect to the reversible hydrogen electrode potential were compared and the oxygen reduction current was determined, it showed 2228 μA / cm ² per unit area of the electrode, and 0 The oxygen reduction current was determined by comparing the current values of the oxygen atmosphere and the nitrogen atmosphere at a potential of .6 V, and it showed 583 μA / cm ² per unit area of the electrode.

11, 21 ... Water tank, 22 ... Raw material tank, 13, 23 ... Liquid feed pump, 14, 24 ... Heater, 30 ... Mixing unit, 40 ... Reactor, 41 ... Internal piping, 44 ... Heater, 51 ... Cooler, 52 ... Filter, 53 ... Back pressure valve, 60 ... Collection container, 110, 210, 220 ... Valve

Claims (4)

A precursor of an electrocatalyst obtained by hydrothermal reaction of a mixture containing the following first material, the following second material, and the following third material in the presence of supercritical or subcritical water, A method for producing an electrocatalyst comprising a step of firing under the condition that the following second material changes to a carbon material:
The first material is one or more metal elements selected from the group consisting of Group 4A elements and Group 5A elements, and one or more selected from the group consisting of hydrogen, nitrogen, chlorine, carbon, boron, sulfur and oxygen A non-metallic element composed of a metal compound,
The second material is a carbon material precursor,
The third material is a nitrogen-containing compound.   The method according to claim 1, wherein the metal element in the first material is Zr or Ti.   The method according to claim 1 or 2, wherein the nitrogen-containing compound in the third material is ammonia.   The method according to claim 1, wherein the firing atmosphere is an oxygen-free atmosphere.

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